1. Field of the Invention
The present invention relates in general to an internal combustion engine having a crankcase ventilation system, and more particularly, to the crankcase ventilation system which discharges blow-by gas from the crankcase by enforcedly introducing fresh air thereinto.
2. Description of the Prior Art
Hitherto, in the field of internal combustion engines, various types of crankcase ventilation systems have been proposed and put into practical use.
Widely used is a type in which fresh air is introduced from an air intake passage upstream of the throttle valve into a crankcase of the engine through an oil separator defined in a cylinder head cover, and blow-by gas in the crankcase, which is thus driven by the fresh air, is introduced into the air intake passage downstream of the throttle valve through another oil separator defined in the cylinder head cover.
This type ventilation system is disclosed in, for example, Japanese Patent First Provisional Publication 58-143109. In this disclosed system, two conduits are provided respectively at front and rear portions of the crankcase, each communicating the interior of the crankcase with that of the cylinder head cover. One conduit is used for the fresh air and the other for the blow-by gas.
However, due to its inherent construction, the ventilation system of this commonly used type has failed to exhibit a satisfied ventilation performance. This is because the power used for driving the blow-by gas is produced by only the pressure difference between the upstream and downstream portions of the air intake passage. Particularly, in the system of the publication, the ventilation effect is very poor because the cylinder head cover used is constructed to constitute therewithin a so-called "bypass conduit" which bypasses the crankcase. In this arrangement, the blow-by gas driving power is not effectively applied to the crankcase.